In a conventional inner rotor-type DC brushless motor having a permanent magnet rotor, an antiscattering cover is attached to the rotor so as to prevent the permanent magnet from scattering.
Conventionally, the antiscattering cover is formed into a cylindrical shape, and its diameter is reduced, by a diameter reduction tool, after a permanent magnet is inserted in the antiscattering cover, so that the antiscattering cover can tightly contact the permanent magnet (see Japanese Laid-open Patent Publication No. 2004-343817); and the antiscattering cover is constituted by an inner cylinder part and an outer cylinder part, the inner cylinder part is composed of a shape-memory metal, and the shape of the inner cylinder part is recovered after a rotor magnet is inserted therein, so that the rotor can be assembled (see Japanese Laid-open Patent Publication No. 2008-29153). Further, plate-shaped permanent magnets, whose length is longer than that of an iron core of a rotor, are provided on an outer circumferential face of the iron core and arranged in the circumferential direction, and the iron core and the magnets are integrated by molding with resin (see Japanese Laid-open Patent Publication No. 2004-147395).
The antiscattering covers of Japanese Laid-open Patent Publications No. 2004-343817 and No. 2008-29153 are capable of preventing the permanent magnets from scattering outward, but they cannot prevent the permanent magnet from scattering in the axial direction. From the aspect of rust prevention, the rotor magnets composed of, for example, neodymium cannot be used in a pump because no antiscattering covers are provided to the both axial ends of the rotor.
In Japanese Laid-open Patent Publication No. 2004-343817, the antiscattering cover is plastically deformed to tightly contact the rotor magnet, so production steps must be increased and the magnet will be easily cracked.
In case that the permanent magnets are integrated by molding as described in Japanese Laid-open Patent Publication No. 2004-147395, a thickness of the resin is added to the outer circumferential face of the rotor, so magnetic gaps between the rotor and stator teeth must be increased and magnetic loss must be also increased.
Further, the magnets will be damaged by molding pressure when an inner part of the ring-shaped magnet is molded with the resin.